Load-controlled hydraulic supply for an attachment attached to an agricultural tractor

ABSTRACT

A load-controlled hydraulic supply for an attachment attached to an agricultural tractor includes a hydraulic high-pressure source providing a volume flow in a supply line, a return line leading to a hydraulic reservoir, and a load-indicating line connected to a device for pressure limiting. The volume flow is adjusted based on pressure feedback prevailing at the load-indicating line.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Patent Application No.102022117880.3, filed Jul. 18, 2022, which is hereby incorporated byreference.

FIELD OF THE DISCLOSURE

The disclosure relates to a load-controlled hydraulic supply for anattachment attached to an agricultural tractor.

BACKGROUND

In recent years an increasing trend toward agricultural attachments withworking functions becoming ever more complex has been observed.Typically, hydraulic actuators in the form of a wide variety ofactuating and/or drive devices are used for carrying out the workingfunctions.

SUMMARY

As the complexity of the working functions increases, generally so doesthe number of required hydraulic actuators, and therefore the number ofhydraulic ports, to be provided on the agricultural tractor for thehydraulic supply thereof. Since the number of hydraulic ports isnaturally limited, what are referred to as power-beyond interfaces aregaining ever more importance. These are standardized in ISO17567 andprovide a requirement-dependent supply of hydraulic consumers, which areconnected thereto, with hydraulic fluid. For this purpose, the hydraulicsupply is designed to be load-controlled as what is referred to as aload-sensing system, wherein the power-beyond interface includes a totalof four hydraulic ports:

-   -   P—supply port    -   LS—load-indicating port for pressure feedback    -   R—return port    -   D—drainage port

The return port, like the drainage port, serves merely for the hydraulicfluid to flow back into a hydraulic reservoir of the agriculturaltractor; the two ports will therefore not be discussed further here. Thefocus is rather on the supply port and on the load-indicating port sincethese ports are crucial for the actual functioning of theload-controlled hydraulic supply. A volume flow adapted in accordancewith the load-indicating pressure prevailing at the return-indicatingport is thus provided by the hydraulic high-pressure source, which canbe a variable displacement pump fed from the hydraulic reservoir, viathe supply port.

Attachments equipped with hydraulic actuators frequently transmit anexcessive load-indicating pressure, i.e. which is inappropriate for theactual supply requirements, to the hydraulic supply via theload-indicating line. This causes the hydraulic supply to generate, andto provide via the supply line, a supply pressure exceeding the actualrequirements of the hydraulic actuators, consequently leading tocorrespondingly inefficient operation.

In view thereof, it is the object of the present disclosure to improve aload-controlled hydraulic supply of the type mentioned at the beginningwith regard to efficient operation.

This object is achieved by a load-controlled hydraulic supply having thefeatures of one or more of the following embodiments.

The load-controlled hydraulic supply for an attachment attached to anagricultural tractor comprises a supply line fed by a hydraulichigh-pressure source, a return line leading into a hydraulic reservoir,and a load-indicating line, wherein the hydraulic supply provides avolume flow, which passes through the supply line, in accordance withpressure feedback prevailing at the load-indicating line. According tothe disclosure, the load-indicating line is connected to a device forpressure limiting.

In this way, it is possible to generate, and to provide via the supplyline, a supply pressure adapted to the actual requirements of thehydraulic actuators. The extent of the pressure limiting is adapted hereto the anticipated hydraulic supply requirements of the hydraulicactuators and is conventionally specific to each attachment model.Associated inefficiencies during operation of the load-controlledhydraulic supply can thus be reliably avoided.

The pressure-compensated control valve can be formed here from acombination of a 2/2-way proportional valve with a pressure-regulatingvalve, wherein the pressure-regulating valve compares an outlet-sidehydraulic pressure with an inlet-side hydraulic pressure at the 2/2-wayproportional valve and sets the outlet-side hydraulic pressure to afixed differential pressure. Thus, the 2/2-way proportional valve keepsthe volume flow emerging from its respective open position substantiallyconstant even in the event of load fluctuations of the hydraulicactuators and/or of operationally induced pressure fluctuations withinthe hydraulic supply. To predetermine the volume flow, the 2/2-wayproportional valve can be brought into its open position via theactuation device, which can be activated, for example, electrically ormechanically, counter to a restoring force produced via a springelement.

Advantageous developments of the load-controlled hydraulic supply aredisclosed herein.

The device for pressure limiting can include a pressure-limiting valveleading into a hydraulic reservoir or a pressure-reducing valve locatedin the load-indicating line.

The pressure-limiting valve is connected on the inlet side to theload-indicating line and is connected on the outlet side to thehydraulic reservoir. When a predetermined pressure threshold value isexceeded, the pressure-limiting valve takes up an open position counterto a restoring force generated via a spring element, and thereforepressure is correspondingly relieved by hydraulic fluid flowing off outof the load-indicating line in the direction of the hydraulic reservoir.

If, for reasons of efficiency, a (further) outflow path in the directionof the hydraulic reservoir is undesirable, the use of apressure-reducing valve instead of the pressure-limiting valve ispreferable in some embodiments. The pressure-reducing valve isprestressed into an open position under the action of a restoring forcegenerated via a spring element and, when a predetermined pressurethreshold value on the outlet side is exceeded, is forced into a closedposition so that further passage of hydraulic fluid is prevented.

The pressure threshold value is predetermined individually depending onthe respective attachment model and is typically of the order ofmagnitude of 100 to 190 bar.

In order to prevent a sudden or uncontrolled drop in pressure in theload-indicating line when the pressure-limiting valve is opened, it isconceivable that the pressure-limiting valve communicates with theload-indicating line via a series-connected flow-limiting element. Theflow-limiting element can be connected here upstream or downstream ofthe pressure-limiting valve in the load-indicating line. Theflow-limiting element is typically an orifice or a throttle.

For example, the device for pressure limiting is adjustable with regardto the predetermined pressure threshold value via a further actuationdevice. In the event that the device for pressure limiting is apressure-limiting valve or a pressure-reducing valve, the furtheractuation device is designed for limiting the restoring force of therespective spring element and, for this purpose, can be activatedelectrically or mechanically.

Furthermore, in the supply line there can be a pressure-compensatedcontrol valve with an actuation device for adjusting the volume flow. Itis possible here to predetermine the volume flow, which passes throughthe pressure-compensated control valve, by corresponding activation ofthe actuation device in such a manner that hydraulic consumers locatedin the agricultural tractor are prioritized. These may relate forexample to safety-relevant hydraulic functions of the agriculturaltractor, for example a hydraulic steering or braking system.

On the other hand, operating situations are also possible in which anundersupply of the hydraulic actuators of the attachment occurs,especially whenever an insufficient load-indicating pressure istransmitted to the hydraulic supply of the agricultural tractor. Undersuch circumstances, it is conceivable for there to be a valvearrangement for variably increasing a load-indicating pressureprevailing externally at the load-indicating line, the valve arrangementraising the load-indicating pressure to a level leading to anappropriate volume flow, typically by up to 40 bar.

For this purpose, the valve arrangement can comprise a 2/2-way valvewhich is pilot-actuated via the externally prevailing load-indicatingpressure, wherein the 2/2-way valve is connected on the inlet side tothe hydraulic high-pressure source and is prestressed into its openposition via an actuating force of a spring element that assists thepilot actuation. The 2/2-way valve therefore forms a booster valve withwhich the extent of the increase in pressure arises directly from therespective actuating force of the spring element. In some embodiments,the actuating force can be changed via an electrically or mechanicallyactivatable actuation device, and therefore an individual raising of theload-indicating pressure is possible, which takes into account thespecific requirements of a particular attachment model.

The use of a pilot-actuated 2/2-way valve as a booster valve leads notonly to a particularly simple construction of the valve arrangement, butat the same time prevents an external admission of contamination via theload-indicating line into the hydraulic supply of the agriculturaltractor. This is because the externally prevailing load-indicatingpressure serves merely for pilot actuation of the 2/2-way valve, butthere is not a direct connection to the hydraulic supply of theagricultural tractor.

In addition, an enable valve designed as a further 2/2-way valve can beconnected in series with the 2/2-way valve, wherein the further 2/2-wayvalve is pilot-actuated via the externally prevailing load-indicatingpressure in such a manner that the further 2/2-way valve takes up anopen position when a predetermined pressure threshold value is exceeded.The further 2/2-way valve ensures that the increased load-indicatingpressure generated via the booster valve is transmitted exclusivelyinternally to the hydraulic supply whenever a corresponding externalsupply requirement (attachment-side) prevails at the load-indicatingline. The pressure threshold value arises here from the restoring forceof a spring element which is dimensioned such that the further 2/2-wayvalve reliably takes up its closed position in the unactuated state. Thepressure threshold value arising to this extent is typically of theorder of magnitude of 2 to 4 bar.

As a result, the load-controlled hydraulic supply according to thedisclosure, within the scope of its different configurations, permits acomprehensive correction of mismatches between the load-controlledhydraulic supply in an agricultural tractor and an attachment-sidehydraulic system, which serves for operating associated hydraulicactuators.

The above and other features will become apparent from the followingdetailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The load-controlled hydraulic supply according to the disclosure for anattachment attached to an agricultural tractor will be described in moredetail below with reference to the drawings. Here, identical referencesigns relate to corresponding components or components which are ofcomparable function. In the drawings:

FIG. 1 shows a schematically illustrated first exemplary embodiment ofthe load-controlled hydraulic supply according to the disclosure, and

FIG. 2 shows a schematically illustrated second exemplary embodiment ofthe load-controlled hydraulic supply according to the disclosure.

DETAILED DESCRIPTION

The embodiments or implementations disclosed in the above drawings andthe following detailed description are not intended to be exhaustive orto limit the present disclosure to these embodiments or implementations.

FIG. 1 shows a first exemplary embodiment of the load-controlledhydraulic supply according to the disclosure.

The hydraulic supply 10 which is schematically illustrated in FIG. 1serves for operating an attachment 14 attached to an agriculturaltractor 12, more specifically for operating at least one hydraulicactuator 18 which is included by an attachment-side hydraulic system 16and is in the form of an actuating and/or drive device 20, depictedrepresentatively as a hydraulic motor and via which an associatedworking function of the attachment 14 can be carried out.

The load-controlled hydraulic supply 10 forms what is referred to as apower-beyond interface with a total of four hydraulic ports:

-   -   P—supply port    -   LS—load-indicating port for pressure feedback    -   R—return port    -   D—drainage port

Each of the hydraulic ports P, LS, R and D merges into an associatedhydraulic line, more specifically into a supply line 24, which is fed bya hydraulic high-pressure source 22, a load-indicating line 26 and areturn or drainage line 30, 32 leading into a hydraulic reservoir 28.

The return port R, like the drainage port D, serves merely for thehydraulic fluid to flow back into the hydraulic reservoir 28 of theagricultural tractor 12; the two ports will therefore not be discussedfurther here. The focus is rather on the supply port and on theload-indicating port P, LS since these ports are crucial for the actualfunctioning of the load-controlled hydraulic supply 10. A volume flowadapted in accordance with the load-indicating pressure prevailing atthe return-indicating port LS is thus provided by the hydraulichigh-pressure source 22, which is a variable displacement pump 34 fedfrom the hydraulic reservoir 28, via the supply port P.

In other words, the load-controlled hydraulic supply 10 forms what isreferred to as a load-sensing system which provides a volume flow, whichpasses through the supply line 24 in the direction of the supply port P,in accordance with pressure feedback prevailing at the load-indicatingline 26.

The attachment-side hydraulic system 16 provided for operating the atleast one hydraulic actuator 18 is connected releasably to theload-controlled hydraulic supply 10 via associated hydraulic hoses orhydraulic couplers 36, 38, 40, 42.

Furthermore, in the supply line 24 there is a pressure-compensatedcontrol valve 44 with a first actuation device 46 for adjusting thevolume flow.

The pressure-compensated control valve 44 is formed from a combinationof a 2/2-way proportional valve 48 with a pressure-regulating valve 50,wherein the pressure-regulating valve 50 compares an outlet-sidehydraulic pressure with an inlet-side hydraulic pressure at the 2/2-wayproportional valve 48 and sets the outlet-side hydraulic pressure to afixed differential pressure. Thus, the 2/2-way proportional valve 48keeps the volume flow emerging from its respective open positionsubstantially constant even in the event of load fluctuations of the atleast one hydraulic actuator 18 and/or of operationally induced pressurefluctuations within the hydraulic supply 10. To predetermine the volumeflow, the 2/2-way proportional valve 48 can be brought into its openposition by electrical activation of the first actuation device 46counter to a restoring force produced via a spring element 52.

Attachments equipped with hydraulic actuators frequently transmit anexcessive load-indicating pressure, i.e. which is inappropriate for theactual supply requirements, to the hydraulic supply 10 via theload-indicating line 26. This leads ultimately to the hydraulic supply10 being caused to generate, and to provide to the supply port P via thesupply line 24, a supply pressure exceeding the actual requirements ofthe hydraulic actuators. In order to prevent the associated losses inefficiency during operation of the hydraulic supply 10, theload-indicating line 26 is connected to a device for pressure limiting54. The extent of the pressure limiting is adapted here to theanticipated hydraulic supply requirements of the hydraulic actuators andis conventionally specific to each attachment model.

According to the first exemplary embodiment of the load-controlledhydraulic supply that is reproduced in FIG. 1 , the device for pressurelimiting 54 comprises a pressure-limiting valve 56 leading into thehydraulic reservoir 28.

The pressure-limiting valve 56 is connected on the inlet side to theload-indicating line 26 and is connected on the outlet side to thehydraulic reservoir 28. When a predetermined pressure threshold value isexceeded, the pressure-limiting valve takes up an open position counterto a restoring force generated via a spring element 58, and thereforepressure is correspondingly relieved by hydraulic fluid flowing off outof the load-indicating line 26 in the direction of the hydraulicreservoir 28.

In order to prevent a sudden or uncontrolled drop in pressure in theload-indicating line 26 when the pressure-limiting valve 56 is opened,it is provided that the pressure-limiting valve 56 communicates with theload-indicating line 26 via a series-connected flow-limiting element 60.For example, the flow-limiting element 60 in the form of an orifice 62is connected in the load-indicating line 26 upstream of thepressure-limiting valve 56, but may also be connected downstream of thepressure-limiting valve 56.

According to a second exemplary embodiment of the load-controlledhydraulic supply according to the disclosure that is reproduced in FIG.2 , the device for pressure limiting 54 comprises, instead of apressure-limiting valve 56, a pressure-reducing valve 64 located in theload-indicating line 26.

The two exemplary embodiments correspond with regard to the remainingcomponents.

The pressure-reducing valve 64 is prestressed into an open positionunder the action of a restoring force generated via a spring element 66and, when a predetermined pressure threshold value on the outlet side isexceeded, is forced into a closed position so that further passage ofhydraulic fluid is prevented.

Both the pressure-limiting valve 56 and the pressure-reducing valve 64are adjustable with respect to the predetermined pressure thresholdvalue via a respective second actuation device 68. For this purpose, thesecond actuation device 68 is designed in such a manner that therestoring force of the spring element 58, 66 can be influenced in atargeted way by electrical activation of the second actuation device 68.

The pressure threshold value is predetermined individually depending onthe respective attachment model and is typically of the order ofmagnitude of 100 to 190 bar.

The above-described measures satisfy operating situations in which anoversupply of the at least one actuator 18 with hydraulic fluid occursbecause of mismatches between the load-controlled hydraulic supply 10and the attachment-side hydraulic system 16. On the other hand,operating situations leading to an undersupply are also possible,especially whenever an insufficient load-indicating pressure istransmitted to the hydraulic supply 10 of the agricultural tractor 12.Accordingly, there is a valve arrangement 70 for variably increasing aload-indicating pressure prevailing externally at the load-indicatingline 26, i.e. at the load-indicating port LS, the valve arrangementmaking it possible to raise the load-indicating pressure to a levelleading to an appropriate volume flow, typically by up to 40 bar.

For this purpose, the valve arrangement 70 comprises a 2/2-way valve 72which is pilot-actuated via the externally prevailing load-indicatingpressure, wherein the 2/2-way valve 72 is connected on the inlet side tothe hydraulic high-pressure source 22 and is prestressed into its openposition via an actuating force of a spring element 74 that assists thepilot actuation. The 2/2-way valve 72 therefore forms a booster valvewith which the extent of the increase in pressure arises directly fromthe respective actuating force of the spring element 74. On the outletside, a pilot actuation of the 2/2-way valve 72 takes place counter tothe actuating force of the spring element 74, and therefore stablepressure conditions arise at the valve.

The actuating force can be changed via an electrically activatable thirdactuation device 76, and therefore an individual raising of theload-indicating pressure is possible, which takes into account thespecific requirements of a particular attachment model.

In addition, an enable valve designed as a further 2/2-way valve 78 isconnected in series with the 2/2-way valve 72, wherein the further2/2-way valve 78 is pilot-actuated via the externally prevailingload-indicating pressure in such a manner that the further 2/2-way valvetakes up an open position when a predetermined pressure threshold valueis exceeded. The further 2/2-way valve 78 ensures that the increasedload-indicating pressure generated via the booster valve, i.e. the2/2-way valve 72, is transmitted exclusively internally to the hydraulicsupply 10 whenever a corresponding external supply requirement(attachment-side) prevails at the load-indicating line 26. The pressurethreshold value arises here from the restoring force of a further springelement 80 which is dimensioned such that the further 2/2-way valve 78reliably takes up its closed position in the unactuated state. Thepressure threshold value arising to this extent is typically of theorder of magnitude of 2 to 4 bar. For example, the further 2/2-way valve78 is connected upstream of the 2/2-way valve 72, but it may also beconnected downstream of the 2/2-way valve 72.

Optionally, an orifice 84 for relieving the load-indicating line 26 ofload in the direction of the hydraulic reservoir 28 is arranged on theload-indicating line 26 next to a filtering element 82, which isarranged directly downstream of the load-indicating port LS and preventsan undesired admission of contamination in the direction of thepilot-actuated 2/2-way valves 72, 78.

The electrical activation of the respective actuation devices 46, 68, 76for a certain attachment model, the activation being required foreliminating possible mismatches between the hydraulic supply 10 andattachment-side hydraulic system 16, takes place via amicroprocessor-controlled control unit 86 (e.g., a controller includinga processor and memory), with the relevant attachment model beingselected via a user interface 88 communicating with the control unit 86.

Proceeding from the illustrations in FIG. 1 and FIG. 2 , the secondactuation device 68 acts mechanically directly on the respective springelement 58, 66 to influence the restoring force. In a departuretherefrom, it may also be provided, however, that a counterforceopposing the restoring force can be generated at the pressure-limitingvalve 56 or at the pressure-reducing valve 64 via the second actuationdevice 68, with there not being a direct intervention in the springelement 58, 66. The same applies to the third actuation device 76 and tothe spring element 74 associated therewith to this extent.

The terminology used herein is for the purpose of describing exampleembodiments or implementations and is not intended to be limiting of thedisclosure. As used herein, the singular forms “a,” “an,” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the any use ofthe terms “has,” “includes,” “comprises,” or the like, in thisspecification, identifies the presence of stated features, integers,steps, operations, elements, and/or components, but does not precludethe presence or addition of one or more other features, integers, steps,operations, elements, components, and/or groups thereof.

Those having ordinary skill in the art will recognize that terms such as“above,” “below,” “upward,” “downward,” “top,” “bottom,” etc., are useddescriptively for the figures, and do not represent limitations on thescope of the present disclosure, as defined by the appended claims.Furthermore, the teachings may be described herein in terms offunctional and/or logical block components or various processing steps,which may include any number of hardware, software, and/or firmwarecomponents configured to perform the specified functions.

Terms of degree, such as “generally,” “substantially,” or“approximately” are understood by those having ordinary skill in the artto refer to reasonable ranges outside of a given value or orientation,for example, general tolerances or positional relationships associatedwith manufacturing, assembly, and use of the described embodiments orimplementations.

As used herein, “e.g.,” is utilized to non-exhaustively list examplesand carries the same meaning as alternative illustrative phrases such as“including,” “including, but not limited to,” and “including withoutlimitation.” Unless otherwise limited or modified, lists with elementsthat are separated by conjunctive terms (e.g., “and”) and that are alsopreceded by the phrase “one or more of” or “at least one of” indicateconfigurations or arrangements that potentially include individualelements of the list, or any combination thereof. For example, “at leastone of A, B, and C” or “one or more of A, B, and C” indicates thepossibilities of only A, only B, only C, or any combination of two ormore of A, B, and C (e.g., A and B; B and C; A and C; or A, B, and C).

While the above describes example embodiments or implementations of thepresent disclosure, these descriptions should not be viewed in arestrictive or limiting sense. Rather, there are several variations andmodifications which may be made without departing from the scope of theappended claims.

What is claimed is:
 1. A load-controlled hydraulic supply for anattachment attached to an agricultural tractor, comprising: a hydraulichigh-pressure source providing a volume flow in a supply line; a returnline leading to a hydraulic reservoir; and a load-indicating lineconnected to a device for pressure limiting; wherein the volume flow isadjusted based on pressure feedback prevailing at the load-indicatingline.
 2. The hydraulic supply of claim 1, wherein the device forpressure limiting comprises one of a pressure-limiting valve leadinginto the hydraulic reservoir and a pressure-reducing valve located inthe load-indicating line.
 3. The hydraulic supply of claim 1, whereinthe device for pressure limiting comprises a pressure-limiting valveleading into the hydraulic reservoir.
 4. The hydraulic supply of claim1, wherein the device for pressure limiting comprises apressure-reducing valve located in the load-indicating line.
 5. Thehydraulic supply of claim 2, wherein the pressure-limiting valvecommunicates with the load-indicating line via a series-connectedflow-limiting element.
 6. The hydraulic supply of claim 3, wherein thepressure-limiting valve communicates with the load-indicating line via aseries-connected flow-limiting element.
 7. The hydraulic supply of claim1, wherein the device for pressure limiting is adjustable with regard tothe predetermined pressure threshold value via a further actuationdevice.
 8. The hydraulic supply of claim 1, wherein in the supply linethere is a pressure-compensated control valve including an actuationdevice for adjusting the volume flow.
 9. The hydraulic supply of claim1, further comprising a valve arrangement for variably increasing aload-indicating pressure prevailing externally at the load-indicatingline.
 10. The hydraulic supply of claim 9, wherein the valve arrangementcomprises a first 2/2-way valve which is pilot-actuated via theexternally prevailing load-indicating pressure, wherein the first2/2-way valve is connected on the inlet side to the hydraulichigh-pressure source and is prestressed into its open position via anactuating force of a spring element that assists the pilot actuation.11. The hydraulic supply of claim 10, wherein an enable valve designedas a second 2/2-way valve is connected in series with the first 2/2-wayvalve, wherein the second 2/2-way valve is pilot-actuated via theexternally prevailing load-indicating pressure in such a manner that thesecond 2/2-way valve takes up an open position when a predeterminedpressure threshold value is exceeded.
 12. A load-controlled hydraulicsupply for an attachment attached to an agricultural tractor,comprising: a hydraulic high-pressure source providing a volume flow ina supply line; a pressure-compensated control valve including anactuation device for adjusting the volume flow in the supply line; areturn line leading to a hydraulic reservoir; a load-indicating lineconnected to a device for pressure limiting including apressure-reducing valve located in the load-indicating line; and a valvearrangement for variably increasing a load-indicating pressureprevailing externally at the load-indicating line; wherein the volumeflow is adjusted based on pressure feedback prevailing at theload-indicating line.
 13. The hydraulic supply of claim 12, wherein thedevice for pressure limiting is adjustable with regard to thepredetermined pressure threshold value via a further actuation device.14. The hydraulic supply of claim 12, wherein the valve arrangementcomprises a first 2/2-way valve which is pilot-actuated via theexternally prevailing load-indicating pressure, wherein the first2/2-way valve is connected on the inlet side to the hydraulichigh-pressure source and is prestressed into its open position via anactuating force of a spring element that assists the pilot actuation.15. The hydraulic supply of claim 14, wherein an enable valve designedas a second 2/2-way valve is connected in series with the first 2/2-wayvalve, wherein the second 2/2-way valve is pilot-actuated via theexternally prevailing load-indicating pressure in such a manner that thesecond 2/2-way valve takes up an open position when a predeterminedpressure threshold value is exceeded.